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Thread: How to add DI duty cycle on 18+ mustang

  1. #1
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    How to add DI duty cycle on 18+ mustang

    In the vcm scanner I have pulse width, start of injection and blend. With the pi side it was easy just add the pulse width for each injector and add a graph for duty cycle. How do I add a duty cycle graph for the di side of things?

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    I could come up with a math channel for gdi but I have to ask why you want it? The gdi injectors are limited by window not by duty cycle, per se.

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    For using as much of the di as possible rather than pi. I want to find its limit for tuning purposes. I'm not turning pi off or anything like that just leaning harder on direct injection.

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    Ok you need to log soi and eoi “intake”, gdi pump duty cycle, and rail pressure (commanded and desired)

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    Quote Originally Posted by engineermike View Post
    Ok you need to log soi and eoi ?intake?, gdi pump duty cycle, and rail pressure (commanded and desired)
    So I have a would not be measuring DC of di injectors but instead the DC of the pump itself

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    Correct.

    When tuning gdi, you will likely be balancing pump capacity and injector period vs window.

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    Port injection duty cycle in terms of events and crank degrees, what does it mean to you?

    To me 100% DC for PI is from an intake valve closing event, 720* of crank rotation, to the next intake valve closing event. You might subtract opening and closing time from that window. So depending on RPM how much would change slighty, but it could be shortly after one IVC to shortly before the next IVC event. You could also move the start of this injection and reduce the window size, it would then be from where ever you moved the start of this injection to the IVC event. Moving the start of the PI injection is usually when you don't want to lose fuel to the overlap and can afford the injection window reduction. This is all independant of the fuel rail pressure.

    So when you ask how do you add/ calculate direct injection duty cycle, I have to ask what is the window of 100% direction injection to you? There are limits in the ECU for the start of injection so that you are not injecting in the exhaust stroke, with the exhaust valve open. If your start of injection is not at this limit do you count the time between start limit and where you started the injection? Then how close to the spark ignition in the compression stroke are you willing to move the EOI clip? The entire injection window is not even 360* of crank rotation or half of what the PI's have. I don't think you can log EOI clip, so a duty cycle calculation would need it manually input. This again, would all be independant of the pressure just how much the injectors are open compared to their maximum, but if you wanted to vary EOI clip based on pressure, it would make it harder.

    You would think with the low side holding the 70PSI, suppling the DI pump with fuel, the DI pump would be more than enough to supply the stock DI injectors fully open through this relatively small injection window. I don't have enough fuel demand on my car to need to use more than just the DI can supply to see, so im taking peoples word for it that the pump lags the injectors. It just hasn't been my experience with fords designs. Stock on gasoline the DI at 90% blend doesn't even get into the compression stroke. Right now as is, I would want bigger DI injectors before an upgrade to the DI pump, just to reduce the injection window further, but get the same mass.
    Last edited by murfie; 2 Days Ago at 02:39 AM.
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    Iirc the stock mustang gt strategy doesn’t allow you to log actual eoi. And you can’t just use the eoi clip in the tune because that number is an input into a more complex equation, the output being a function of eoi clip but not equal to eoi clip. I believe you can log soi and effective pulsewidth, and from that and rpm you can calculate eoi, but I’m not sure how accurate it will be.

    On the Whipple os you can log eoi in deg of crank angle for all 8 cylinders individually. I was able to determine that the injectors will support more than the stock pump can supply, but only by about 10%. I’ve also learned that you can inject up to about 110 deg btdcC before you start losing power.

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    At some point HPT added logging all 8 EOI for a stock strategy. PIDs are under engine> fuel> injection timing for selection. using a max of 360 and min of 0, you should see the intake and compression stroke seperated in the middle at 180*. I was doing 540* max with some math on the cam angles so I could see valve events, DI, and spark advance all on the same chart. I started out looking at it from the cam angle degrees, but people seem to understand spark advance degrees better than cam angle degrees.

    My math was as close as a ~.5ms open/close delay could let me be when I had to calculate it.
    ([7924.161])-(([6348.254]-.5)*([50070.56]*.006)))

    .006 comes from 360* per rev / 60,000ms per minute to get * per ms. Then when multiplied by pulse width in ms you are left with a pulse width in degrees.
    Last edited by murfie; 2 Days Ago at 03:53 PM.
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    Quote Originally Posted by murfie View Post
    At some point HPT added logging all 8 EOI for a stock strategy. PIDs are under engine> fuel> injection timing for selection. using a max of 360 and min of 0, you should see the intake and compression stroke seperated in the middle at 180*. I was doing 540* max with some math on the cam angles so I could see valve events, DI, and spark advance all on the same chart. I started out looking at it from the cam angle degrees, but people seem to understand spark advance degrees better than cam angle degrees.

    My math was as close as a ~.5ms open/close delay could let me be when I had to calculate it.
    ([7924.161])-(([6348.254]-.5)*([50070.56]*.006)))

    .006 comes from 360* per rev / 60,000ms per minute to get * per ms. Then when multiplied by pulse width in ms you are left with a pulse width in degrees.
    Can you explain like I'm 5 why direct injection has a "window" to inject that is smaller than port?

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    You only want to inject between about 30 deg atdc-intake and 110 deg btdc compression. That’s the window. Counting in reverse from tdc combustion, the window would be about 330 to 110, or 220 deg total out of a 720 deg cycle.

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    But why is it restricted to a narrower window than port injection?

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    Direct injection means you are injecting fuel directly into the cylinder, so what the guys above are trying to explain is the window in which you can inject fuel is limited to intake stroke and compression stroke. Injecting fuel during combustion stroke and exhaust stroke probably a bad idea.

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    Versus port injection you could theoretically inject fuel 100% of the time because all the injecting is happening before the intake valve.

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    I understand the reason for spraying in that window but why is port injection any different? Would not want to deliver fuel into the cylinder at that same window no matter what

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    I think I understand now.

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    What happens when you inject fuel into the intake port during the exhaust stroke? What happens if you inject fuel into the cylinder during the exhaust stroke? Big difference.

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    Trying to compare the windows directly to one another is confusing with out thinking about 5 strokes of the piston before the power event being compared. Does this image help?

    PI vs DI injection windows compared.jpg

    The two injection windows are offset from one another.
    PI vs DI injection windows compared.jpg
    Last edited by murfie; 1 Day Ago at 10:46 PM.
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  19. #19
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    Thank you